In the manufacture of integrated circuits, integrated circuit packaging, and hybrid circuits, it is necessary to test the circuits as part of the manufacturing process. The testing is performed by creating a temporary electrical contact between a test probe or probes with selected points on the circuit under test. A predetermined programmed test is then undertaken utilizing signals applied to the circuit and derived therefrom through the probes. Because of the complexity and the small size of the circuits, particularly extremely compact integrated circuits, the numbers of contacts that must be made with the circuit for appropriate testing demands strict control over the positioning of contact probes; further, the force with which the probes are placed against the predetermined circuit pads or points is extremely important. Controlling the precise positioning of the probes as well as the force on each probe demands extreme accuracy in the manufacture of probe systems.
In the prior art, such probe systems have typically used probes, which are normally in the form of very fine needles, that are individually attached to a printed circuit card by either soldering the probe directly to the printed circuit board or to a holding device which in turn is soldered to the printed circuit card. It has been suggested in the prior art that a blade such as the type described in U.S. Pat. No. 4,161,692 be secured to a printed circuit card with needles or probes attached to the end of the blade. The probes typically extend from the mounting place such as the blade in a cantilever arm fashion reaching out as much as several hundred mils to the point on the circuit, the pad, to be probed. To change the force on the probe requires either changing the probe diameter to make the probe stiffer or more flexible, or changing the probe length or cantilever length. Further, the utilization of such probes does not provide a convenient means for implementing a controlled impedance transmission line; that is, in many high frequency test environments, the use of transmission line techniques is very important for the accuracy and validity of the test.
Prior art probes that are cantilevered, or extend any significant distance from a supporting surface, are relatively free to drift; that is, they can become misaligned and will no longer contact the desired pad on the device for test. If the circuit to be tested contains contact pads that are in a single plane, it is possible for prior art probes to drift out of planarity such that the force existing between a given probe and its corresponding contact pad may be significantly greater or lesser than a probe and its corresponding pad at a different location on the circuit under test. Further, using such prior art techniques, it is very difficult to probe pads that are on different planes on the device being tested; for example, in some hybrid circuit conformations, it is possible to have pads or signal runs or traces that are difficult to properly contact using probe technologies of the prior art.
A further difficulty with prior art probe systems, relates to the means by which the probes are connected to the probe mounting card or circuit board. The connection of the probe is usually made by soldering the probe directly to the printed circuit board. The soldering process requires the use of flux which is frequently difficult to remove and can cause electrical leakage problems when the system is in use. This problem is greatly exacerbated in those instances where very high probe density is required. In the event a probe or probes become damaged, it is desirable to repair the probe rather than discard the entire assembly. However, removal and replacement of probes in such an environment becomes extremely difficult, time consuming, and very expensive.